LANDMARK OF GEOLOGY IN THE EAST MIDLANDS Breedon Hill Breedon Hill forms one of the most prominent features in the landscape of north-west Leicestershire, standing up 50 m above the surrounding ground. That it has been a major landmark throughout recorded history is suggested by its name, which is derived from the Celtic ‘bre’ and the Anglo-Saxon ‘dun’, both words meaning ‘hill’. Viewed from the east, the rugged vertical western quarry face is crowned by the church that looks very precarious; it stands about 70 m behind Breedon quarry seen from the viewing platform. The rocks in the right foreground are the massive mud-mound reef the quarry face, but looks much closer from a distance. dolostones. On the left side of the quarry are well bedded, To see the quarry and its geology at relatively close steeply dipping dolostones which, in the distance, show quarters, the viewing platform at the north end of the gentle folding. The cave with its red-brown Triassic fill can quarry should be visited. There is also a footpath that be seen to the left of the foreground tree in blossom. follows the quarry’s eastern rim. Quarry visits are limited to organized groups, but a few small exposures Breedon Hill is one of six inliers of the Peak are present along the footpath from Breedon village up Limestone Group (informally known as the the western slopes of the hill. Carboniferous Limestone) in north west Leicestershire. The others are at Cloud Hill, Barrow Hill, Osgathorpe and Grace Dieu; all have been quarried in the past but the only other operating quarry is at Cloud Hill, just over a kilometre south of Breedon Hill. Cloud Hill is the larger quarry and is currently the only producer of aggregate. All these inliers are surrounded by rocks of Triassic age, with Precambrian Charnian rocks also abutting on the south side of the Grace Dieu inlier. Other inliers of these limestones occur 3-4 km to the west, around Ticknall, Calke Abbey and Dimminsdale in south Derbyshire. The Breedon carbonates The geology of Breedon Hill has been summarised in several publications, including Fox Strangways (1905), Parsons (1918), Mitchell and Stubblefield (1941), Ambrose and Carney (1997) and Carney et al. (2001, 2002). The Breedon story starts in the early Carboniferous, in Early Chadian times, when much of England was enveloped in a warm tropical sea close to the equator, where carbonates were deposited to form the Peak Limestone Group. Breedon Hill and Cloud Hill, lay on the Hathern Shelf, just south of the Widmerpool half-graben (or ‘gulf’), a deep, fault- bounded Carboniferous basin. Its location and evidence from sediments in the quarry suggest that Breedon was just on the flanks of the half-graben, in deeper water than most of the shelf area, and in water slightly deeper than that at Cloud Hill. But deposition at both quarry sites followed the same general pattern. The earliest rocks are the Milldale Limestone Formation, which consists mostly of the well-bedded, generally fine-grained carbonates, now dolostones, deposited by storms, possibly with some turbidite development. In quiet periods, fine muds and silts settled out from suspension to form partings between the carbonates. The geology of Breedon Hill (by British Geological Survey). These storm deposits in Breedon quarry generally yield MERCIAN GEOLOGIST 2013 18 (2) 139 The northern end of the quarry with red-brown Triassic sediments lying unconformably over the steeply dipping Carboniferous carbonates. The red colour of the limestone on the left side of the upper bench is the result of groundwater re-depositing iron oxide carried down from the overlying Triassic rocks.

only a few crinoids and brachiopods, but the paucity of additionally yielding corals, nautiloids, and ammonoids. fossils may be due to the later dolomitisation process This unbedded dolostone has been interpreted as a that has affected all the rocks in Breedon, and may have mud-mound reef, which formed by micro-organisms destroyed fossil remains. The thickness of the Milldale secreting a carbonate mud that built up into a mound Limestone at Breedon is around 400 m. (or reef). The reef at Breedon has been likened to those The rock that indicates water depth occurs on the in Derbyshire, where all the Early Chadian reefs are west face of the quarry, where a very fine-grained, of a Waulsortian reef facies, known to occur in water massive dolostone has no internal bedding structures. depths of 220-280 m (Bridges and Chapman, 1988). It is also more fossiliferous than the storm carbonates, On the northern face of the quarry, similar well-bedded dolostones with the same fauna are interpreted as the reef flank, with debris cascading off the reef and building up in beds. Found in this part of the sequence, the ammonoid Fascipericyclus fasciculatus indicates an Early Chadian age. The only other age-diagnostic fossils found in Breedon quarry are the brachiopod Levitusa humerosus and a microfauna in layers of chert nodules within the storm carbonates. These nodules were unaffected by the dolomitisation and the microfauna has been preserved. Both indicate the same Early Chadian age. Cloud Hill quarry is the type locality for the brachiopod Levitusa humerosus. Other mud-mound reefs are seen in Cloud Hill quarry but these formed in shallower water of probably around 100 m depth, as fringing reefs on the Hathern Shelf. Two important features occurs on the north face of Breedon quarry. An unconformity lies within the Peak Limestone, although the position of it is not precisely known. It represents a time gap of around 10 million years, separating the Early Chadian Milldale Limestone from the Holkerian-Asbian Cloud Hill Dolostone Formation. The latter is known from a fallen block that contained a coral of this age. A bedding plane crowded with the trace fossil Thallasinoides, which indicates a prolonged period of bioturbation, has provisionally been taken as the unconformity base in Breedon quarry. These younger beds and the unconformity are well exposed in Cloud Hill quarry, where a pronounced angular unconformity has been well exposed over time and has been named the ‘Main Breedon discontinuity’ (Carney et al., 2001). At the top of the north face of Breedon quarry, there is a major unconformity with the The quarries of Breedon Hill and Cloud Hill, either side of younger Triassic rocks exposed. This represents a time the curving M42 motorway (from Google Earth). gap of around 100 million years. 140 MERCIAN GEOLOGIST 2013 18 (2) Dolomitisation and mineralisation Karst and cave development The carbonate rocks at Breedon have been pervasively Karst development in the form of caves and small altered by the conversion of the original calcite to the voids is another feature of the rocks in Breedon quarry. magnesium-rich dolomite and the rocks are now referred Again, the timing of their formation is not known to as dolostones. The timing of this process is not fully precisely but there are several clues. The 15% volume known, though an early, pene-contemporaneous stage reduction of the rock resulting from the dolomitisation and a later stage of Triassic age have been suggested process may have played a significant part. Many of (Parsons, 1918). Evidence from mapping the quarries the smaller voids are lined with dog-tooth spar calcite showed that the dolomitisation occurred before the associated with the end-Carboniferous mineralisation, Triassic, as fragments of dolostone occur within caves so they formed probably quite soon after deposition of and voids infilled with Triassic sediments. It is very the carbonates and probably in response to circulating likely that the dolomitisation occurred in the latest ground waters. Widening of some of the larger caves Carboniferous times, when the area was subjected could have occurred throughout the Permian. Many to higher temperatures, pressures and mineralisation were formed by Early Triassic times at the latest, as associated with the Variscan orogeny. some are infilled with sediments of Mercia Mudstone Mineralisation has occurred in two phases in these Group age. Further cave enlargement may be attributed rocks. The earlier, in the Late Carboniferous (King, to groundwater flow during the Quaternary. 1968, 1980, 1982, 1983), resulted in the deposition Perhaps the most striking karstic feature lies in the of calcite as a gangue mineral along with a variety of east face of Breedon quarry, where a large cave has been other minerals of which the most common is galena. completely infilled with Triassic sediments. It is about Others found include wulfenite and cinnabar. The 60 m wide and 10 m high, and the roof slopes into the second phase occurred in the Triassic, associated quarry at around 40º. The sediments infilling the cave with fluids moving along the unconformity. These left are dominantly massive red-brown siltstones, with mainly copper minerals; none has been seen at Breedon some included clasts of finer and commonly laminated because the unconformity is inaccessible, but they are mudstones. These represent rapid deposition from common at Cloud Hill. water flowing into the cave. The uppermost deposit in the cave is a thin finely laminated, waterlain bed of sandstone-siltstone/mudstone couplets. The most likely timing for the infilling of the cave is during deposition of the Tarporley Siltstone Formation, the basal unit of the Mercia Mudstone Group. Laminated mudstone forming the cave deposit clasts commonly occurs in this formation, and the depositional environment is a flat alluvial plain washed by streams, so there was abundant water that could wash into the cave. Indeterminate bone fragments have been found in the cave fill (Fraser, 1994). Development of the Breedon landscape The landscape of Breedon Hill has its origins dating back some 300 million years to the late Carboniferous Variscan orogeny, when earth movements in the Cavity in the limestone infilled with dog-tooth spar calcite, indicating that the caves pre- date the late Carboniferous mineralisation.

The cave exposed in the quarry, before it was more overgrown, with its Triassic fill of red- brown siltstones of the Mercia Mudstone Group. MERCIAN GEOLOGIST 2013 18 (2) 141 Midlands microcraton, pushed the Early Carboniferous limestones up into their near vertical aspect now exposed in Breedon and Cloud Hill quarries. The regional dip is to the west but the rocks are commonly overturned at Breedon and dip to the east. Erosion during the Permian removed younger Carboniferous rocks of the Millstone Grit and Pennine Coal Measures groups, leaving low hills of the Peak Limestone. Breedon Hill was probably somewhat higher than it is today. About 250 million years ago, in the Triassic, Breedon Hill was surrounded by the river system that deposited the Sherwood Sandstone Group, with the river flowing from northern France across much of England. This river had two courses, with a divergence somewhere in the English Midlands. It flowed north along the western side of England through the Staffordshire and Cheshire basins and into the East Irish Sea Basin, and also along the eastern side, through Nottinghamshire and Yorkshire and out into the North Sea, but it is unlikely that it occupied both courses at the same time. A block of Breedon Breccia with matrix-supported clasts, which formed as debris flows on the side of the Triassic hill. About 10 million years later, the river ceased flowing, leaving a broad flat alluvial plane that was accumulation on the plains reached its level, surface washed by river channels and contained many lakes; water washed sediment into the cave. its deposits are the Tarporley Siltstone Formation at Eventually, towards the end of the Triassic, Breedon the base of the Mercia Mudstone Group. Following Hill, Cloud Hill, Mountsorrel and Charnwood Forest this, desert conditions set in. Much of England was a were completely buried. A prerequisite for this burial low-lying and flat landscape, with hills like Breedon was continued regional subsidence (Carney, 2007) and Mountsorrel standing up as inselbergs. Charnwood which favoured preservation of the soft desert muds. Forest formed a range of low, craggy hills that were But this was not the end of sedimentation. Regional probably mountains in the earliest Triassic. The desert subsidence continued throughout the Jurassic and was not a sandy desert like parts of the modern day Cretaceous; Breedon Hill was under the sea and a great Sahara, but a pelleted clay particles or ‘dust’ desert. thickness of marine sediments accumulated on top of Modern day analogues include the parna of southern the Triassic strata. When the sea finally retreated at Australia (Jefferson et al., 2002). Clouds of dust blew the end of the Cretaceous, the area was uplifted and across the flat plain and accretion occurred because of tilted, and a long period of erosion ensued throughout a high water table and frequently damp ground surface. the Palaeogene and Neogene. All of the Cretaceous This also resulted in the precipitation of gypsum close and Jurassic rocks were stripped off, together with to the ground surface. some of the Triassic, leaving behind the more resistant As the layers of sediment built up, Breedon Hill dolostones. Breedon Hill’s Permo-Triassic expression was gradually buried. The heavy rains that resulted as an inselberg is thus being revealed once again. What in the deposition of the fine sandstones and siltstones was left prior to the Quaternary glaciations is pure guess on the desert plains had their impact on Breedon Hill. work, but the Breedon Hill of today was trimmed by Screes that built up on the hillside were mobilised and the passage of glaciers particularly during the Anglian flowed down the hill as debris flows. These survive glaciations of around 440 000 years ago. in the quarry as fallen blocks of dolostone breccias. They are all matrix-supported, indicating deposition in Quarrying at Breedon debris flows, as opposed to clast-supported screes. The Breedon quarry has been working since around the infilled cave now exposed in the quarry face had an 1880s, and there is evidence of earlier quarrying going opening on the surface of the hill. When the sediment back hundreds of years. At the present time, quarrying activities are limited, with only a few thousand tons extracted each year, all for ornamental stone. In the past the limestone has been extensively used as roadstone, as is much of the current Cloud Hill output. The quarry has also produced agricultural lime, fluxing stone, rockery, walling and edging stone, flux for blast furnaces and foundries, tarred and bituminous aggregate, foundation stone and top-dressing for tennis courts. In the past, the Profile through Breedon Hill; colour keys as on the map; variety of colours of the stone at Breedon and Cloud Hill vertical scale is double the horizontal scale. quarries have been used for surfacing driveways and 142 MERCIAN GEOLOGIST 2013 18 (2) paths. Products have included the self-binding Breedon Golden Amber Gravel, which has been used for the garden pathways at Chatsworth House, in Derbyshire; this gravel is self-setting under treatment by water and roller. Much of the quarry overburden has been used around the village and to create the village green. Planning permission has been granted for an eastward extension of the quarry into the neighbouring field, which will necessitate rerouting of the road from Breedon to Wilson. This should reveal more of the course of the cave that is infilled with Triassic sediments. There is a good possibility of finding animal bones on the cave floor as it is exposed, and these could even indicate what Chirotherium really looked like. This mysterious animal is, to date, only known from Tomb carved from local alabaster within Breedon church. footprints, found mainly in the Sherwood Sandstone but also in the Mercia Mudstone Group, up until Late Lincolnshire Limestone, sourced from at least 40 km Triassic Carnian times. away to the east. Another geological gem inside the church is a tomb carved from local alabaster, a tough Breedon Church variety of gypsum, sourced locally, either from Fauld, Chellaston or Aston, and carved in Burton upon Trent No visit to Breedon would be complete without a where an alabaster industry was well established. visit to the fine 12th century church of St. Mary and St. Hardulph, which crowns the hill, and constitutes References another treasure trove of geological features. Ambrose, K. & Carney, J.N. 1997. Geology of the Breedon on the Surprisingly, it is built not of the local rock nor even Hill area. Brit. Geol. Surv. Tech. Rept., WA/97/42. Anon., 1958. Breedon and Cloud Hill quarries. Quarry Managers’ of the Millstone Grit sandstones from the Melbourne Journal, 89-94. area, but from Bromsgrove Sandstone, part of the Bridges, P.H. & Chapman, A.J., 1988. The anatomy of a deep water Sherwood Sandstone Group. This crops out in many mud-mound complex to the south west of the Dinantian platform in areas nearby but the precise source used is not known. Derbyshire UK. Sedimentology, 35, 139-162. A wide variety of rocks have been used for headstones Carney, J.N., 2007. Geological evolution of Central England with reference to the Trent Basin and its landscapes. Merc. Geol., 16, in the graveyard, but most striking are the slates. Up 231-240. to around the middle of the 19th century, the locally Carney, J.N., Ambrose, K. & Brandon, A., 2001. Geology of the quarried Swithland Slate provided all the headstones, country between Loughborough, Burton and Derby. Brit. Geol. but improved transport links made the cheaper and Surv. Sheet Description, Sheet 141. better Welsh slate more accessible, and this led to the Carney, J.N., Ambrose, K. & Brandon, A., 2002. Geology of the Loughborough district: a brief explanation of geological sheet decline and eventual collapse of the Swithland industry. 141 Loughborough. Brit. Geol. Surv. Sheet Explanation, Sheet 141. Apart from the dates on the graves, the two slates are Fox Strangeways, C., 1905. The geology of the country between readily distinguished; the Swithland Slate, because of Derby, Burton-on-Trent, Ashby-de-la-Zouch and Loughborough. its relatively poor cleavage, has a rough back surface, Mem. Geol. Surv. G.B., Sheet 141. whereas the much better cleaved Welsh slates have Fraser, N.C., 1994. Assemblages of small tetrapods from British Late Triassic fissure deposits. 214-226 in Fraser, N.C. & Sues, smooth front and back surfaces. H-D. (eds.), In the shadow of the dinosaurs: Early Mesozoic Breedon Hill was home to an Anglo-Saxon tetrarapods. Cambridge University Press. monastery, founded in about AD 676. When this fell Jefferson, I.F., Rosenbaum, M.R. & Smalley, I.J. 2002. Mercia Mudstone as a Triassic aeolian desert sediment. Merc. Geol., 15, into disrepair, some of the carvings were rescued and 157-162. placed in the church; they were carved in the Jurassic King, R.J., 1968. Mineralization. 112-137 in Sylvester-Bradley, P.C. & Ford, T.D. (eds.), The Geology of the East Midlands, Leicester University Press. King, R.J., 1980. Wulfenite in Leicestershire. Trans. Leicester Lit. Phil. Soc., 72, 51-58. King, R.J.. 1982. The occurrence of cinnabar in Leicestershire. Trans. Leicester Lit. Phil. Soc., 76, 51-53. King, R.J., 1983. The occurrence of galena in Leicestershire. J. Russell Soc., 1, 27-47. Mitchell, G.H. & Stubblefield, C.J., 1941. The Carboniferous Limestone of Breedon Cloud, Leicestershire, and the associated inliers. Geol. Mag., 78, 201-219. Parsons, L.M., 1918. The Carboniferous Limestone bordering the Leicestershire Coalfield. Q. J. Geol. Soc., 73, 84-110.

Breedon church, with its gravestones of rough-backed Keith Ambrose Swithland Slate and smooth-backed Welsh Slate. British Geological Survey, [email protected] MERCIAN GEOLOGIST 2013 18 (2) 143